Wireless mobile devices such as cellular phones are getting smaller and in the mean time the number of antennas needed in a device is getting greater. For instance, a typical modern mobile phone has both primary and diversity antennas for enhanced overall WWAN performance. Also, WLAN, Bluetooth, GPS and TV broadcasting (e.g. MediaFlo) all require antennas. Consequently, a typical device may require as many as eight or more antennas in a single device. Multi-band antenna can be used to substantially reduce the antenna count. Optimizing an antenna design so as to keep antenna count low and antenna size small is very challenging. In general, small volume degrades antenna performance while multiple antennas in proximity increase mutual coupling.
Common approaches to the design of multi-band antennas for use in mobile devices include two-dimensional (2D) and three-dimensional (3D) antenna structures of various geometries, the latter being, in many cases, manufactured simply by folding the 2D designs in 3D for decreasing their dimensions. This approach increases the profile dimension of the 3D antenna, which is then determined by the RF coverage of the antenna, the resulting clearance to the ground-reference structure and the dielectric loading effect.
Other efforts used to design compact multi-band antennas include the use of complex electro-mechanical switches (MEMS) to alter antenna geometry and match characteristics to the required RF bands. However, despite good performance, such approaches suffer from the need for matching circuits, increased complexity and cost of manufacture.
An alternative solution involves double grounding planes. Again, the improved performance comes at the penalty of suitability for clam-type mobile devices where the two ground planes can be easily implemented and integrated in the two separate parts of the clam-phone, with their adjoining hinge serving to accommodate the main part of the antenna. This approach still leaves the problem of finding a suitable antenna to support the multi-band need of the more common single-block smart phones.
Preferred approaches include planar inverted F antenna (PIFA) structures. These are the most popular for use in (non-clam-type) mobile phones due to their low profiles. However, conventional PIFA designs only support two or three RF bands. More recent designs can support four and some even five RF bands, the latter commonly referred to as penta-band. For acquiring wide bandwidth, as well as, multi-band properties in PIFA, several multi-resonance techniques using stacked patches, additional parasitic resonators, multi slots, harmonic resonances of meander line, and a slot between feed and shorting pins have been used.
Such antenna configurations unfortunately all suffer from drawbacks. For example, typical multi-band, and particularly, penta-band, PIFA designs are typically too bulky and unsuitable for small devices. Often dimensions are too large, awkward for desired clearances for activation keys and buttons in the appropriate positions, and/or do not provide clearance for easy integration of additional mechanical elements.
There is a need for a multi-band antenna with improved radiation efficiency across as many as five RF bands, having compact dimensions, suitable for use in a common type of mobile device, and easy and cheap to manufacture. The required antenna should fulfill all these needs for a −5 db or −6 db return loss as opposed to existing designs where there is a compromise in one or more requirements.
To facilitate understanding, identical reference numerals have been used where possible to designate identical elements that are common to the figures, except that suffixes may be added, where appropriate, to differentiate such elements. The images in the drawings are simplified for illustrative purposes and are not necessarily depicted to scale.
The appended drawings illustrate exemplary configurations of the disclosure and, as such, should not be considered as limiting the scope of the disclosure that may admit to other equally effective configurations. Correspondingly, it has been contemplated that features of some configurations may be beneficially incorporated in other configurations without further recitation.